A. Field of the Invention
This invention relates to a security feature and a method for checking the security feature. Such security features are used for safeguarding value documents, in particular for authenticating the value documents.
B. Related Art
For safeguarding value documents, the latter are equipped with security features and/or with security elements having security features in order to make it possible to check the authenticity of the value document. The security features and security elements serve as protection from unauthorized reproduction of the value documents. As security elements there are used for example security threads or foil elements which are connected to a value document. The security features can be connected to the substrate of the security element or to the substrate of the value document itself.
As security features there are employed for example luminescent pigments which consist of a host lattice doped with a luminophore. Optical transitions of the luminophores lead to a luminescence of the luminescent pigment. For the authenticity check of a value document having the luminescent pigment, it is checked for example whether the value document has the desired luminescence and it is decided in dependence thereon whether or not the value document is authentic.
To make it more difficult to imitate the value documents, the latter are provided with a security feature made of a luminescent pigment which, upon corresponding optical excitation, shows a characteristic luminescence spectrum with several luminescence peaks. However, the luminescence spectrum of such a security feature can in some cases be simulated by another luminescent pigment which does not deliver the identical luminescence spectrum to the security feature, but a similar one. To obtain a sufficiently similar luminescence spectrum, it is not absolutely necessary to hit upon the identical chemical composition of the luminescent pigment. For slight deviations from the chemical composition of the security feature usually do not have a strong effect on the obtained luminescence spectrum.
An object of the present invention is hence to specify a security feature with a luminescent pigment whose luminescence spectrum is difficult to imitate.